The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Light detection and ranging (lidar) is a technology that can be used to measure distances to remote targets. Typically, a lidar system includes a light source and an optical receiver. The light source emits light toward a target which then scatters the light. Some of the scattered light is received back at the receiver. The system determines the distance to the target based on one or more characteristics associated with the returned light. For example, the system may determine the distance to the target based on the time of flight of a returned light pulse.
A typical lidar system is configured to wait for the scattered light to return during a certain fixed period of time tmax corresponding to the time it takes a light pulse to travel the maximum distance at which the lidar system is configured to detect targets, and back. For example, the lidar system may be configured to detect objects up to 200 meters away, and tmax accordingly can be approximately 1.33 μs. After tmax, the lidar system generates the next light pulse.
In some cases, however, an emitted pulse of light is scattered by atmospheric obscurants to produce a spurious return. In particular, the lidar system detects a return pulse that appears to represent a solid object at a location where no solid objects are present. Further, atmospheric obscurants in some cases only partially scatter a pulse of light, and the remaining portion of the pulse of light reaches a target within the maximum range of the lidar system. The emitted pulse in this case corresponds to multiple returns during the same ranging event. Still further, a highly reflective object located beyond the maximum range of the lidar system can generate a return that the lidar system detects only during a subsequent ranging event, after a new pulse of light is emitted, resulting in the so-called “range wrap” problem. Highly reflective objects can also cause spurious returns when a pulse is reflected multiple times between emission and detection. For example, an emitted pulse may reflect from a puddle on the road, then reflect from a target, then from the puddle again, before reaching the detector. Such returns can be classified as “multi-path” returns. Additionally, a lidar system can receive a scattered pulse originating at a different lidar system and generate a return that can be classified as interference. Analogously, when a lidar comprises multiple optical heads and/or detectors, a lidar pulse that was intended for reception by one detector may reach another detector, generating a return that can be classified as cross-talk.